276 
FXUS66 KLOX 140643
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA 
1143 PM PDT Tue Jul 13 2021

.SYNOPSIS...13/136 PM.

A cooling trend will bring temperatures down to near to slightly
below normal by mid to late week as high pressure weakens over 
the west coast and onshore flow increases. Coastal night through 
morning low clouds will work their way into the coastal 
valleys by Wednesday. A minor warming trend is expected over the
weekend into next week.

&&

.SHORT TERM (TUE-FRI)...13/910 PM.

***UPDATE*** 

This morning, isolated convective rain showers/storms formed from
L.A. to Santa Barbara County, with most of the activity focused 
on the L.A. metro area. Downtown received 0.10", which makes this
the fifth wettest July on record. This evening, marine layer 
clouds are increasing in coverage, and have already begun to push
into a few coastal areas. No significant changes have been made 
to the forecast, and high temperatures for Wednesday afternoon 
look on track. A few spots may be a bit warmer over Ventura and 
L.A. County Wednesday, as it will be sunnier. 
 

***From Previous Discussion***

Clouds and showers have been slow to dissipate today across
LA/Ventura Counties after dropping light rain amounts in short but
moderate to heavy bursts earlier today. Expecting to continue to
see clouds dissipating through the afternoon but can't rule out a
stray shower, especially in the mountains.

The remainder of the forecast is largely unchanged. The cooling
trend that began Monday will continue through the end of the 
week, though many parts of LA/Ventura Counties will see a bump in 
temps Wednesday after today's unexpected clouds and showers 
prevented temps from reaching their full (clear sky) potential.
Onshore flow expected to get a little stronger each day through
Friday which will also help pull marine layer stratus a little
farther inland during the early morning hours. Some coastal/valley
areas will be back to normal or even a little below normal as 
early as Tuesday and those trends will reach the mountains and far
interior areas Wednesday and Thursday. By Thursday most areas will
be at least 1-3 degrees below normal and as much as 4-8 degrees
below normal for interior SLO County and some of the coastal
valleys.

.LONG TERM (SAT-TUE)...13/147 PM.

High pressure near the four corners is expected to start building
again Sunday into early next week. This one will be centered
farther north and east than the last heat wave so the warming
trend will not be as significant as before. However, temperatures
are expected to climb back above 100 across the Antelope Valley
and close to 100 for the warmer coastal valleys. Onshore flow will
remain in place though it will be weakening with time so some
warming is expected for coastal areas as well, though the marine
layer will still have a significant role there.

Potentially the bigger story next week will be the increase in
monsoon moisture as both models show a couple of tropical systems
moving off Mexico into the Pacific. Upper level flow around the 4
corners high will be favorable for moisture advection into the
area and if those tropical systems develop and track as models
expect there's a reasonable chance that southwest California will
see increasing humidity and shower/thunderstorm chances as early
as Sunday or Monday, but more likely Tuesday and Wednesday. Not
quite enough confidence this far out to go with thunderstorms yet
but if projections remain the same over the next few days will
likely start adding pops to the forecast. In these scenarios
showers/storms are not always just confined to the mountains and
deserts.

&&

.AVIATION...14/0642Z.

At 2315Z, the marine inversion at KLAX was based at 1100 feet.
The top of the inversion was 3500 feet with a temperature of
26 degrees Celsius.

Good confidence in inland TAFs (KBUR and KVNY have a 20 percent
chance of IFR cigs 13Z-16Z).

Moderate confidence in coastal TAFs Low clouds will move into all
coastal sites by 12Z and will clear away by within +/- 45 minutes
if fcst. Lower confidence again after 00Z due to uncertainty in
arrival of low clouds.

KLAX...Moderate confidence in TAF. There is a 30 percent chc of
OVC010 conds after 12Z. There is a 30 percent chc of clearing at
17Z. Low clouds may not return until 15/07Z. Any easterly wind 
component will be 3 kt or less.

KBUR...Good confidence in AF. There is a 20% chance of OVC006 
13Z-16Z.

&&

.MARINE...13/803 PM.

For the Outer Waters, moderate to high confidence in current 
forecast. Through Thursday afternoon, winds and seas will remain 
below SCA levels. For Thursday night through Sunday there is a 
50%-60% chance that winds will increase to SCA levels, starting in
the northern zone (PZZ670) Thursday night and spreading south of
Point Sal to the Channel Islands by Friday evening.

For the Inner Waters north of Point Concpetion, moderate to high
confidence in current forecast. High confidence in winds and seas
remaining below SCA levels through Fri night. For Saturday and
Sunday, there is a 50% chance of SCA level winds mainly during 
the afternoon and evening hours. 

For the Inner Waters south of Point Conception, moderate to high
confidence in current forecast. There is a 30%-40% chance of SCA 
level gusts across the western half of the Santa Barbara Channel 
Friday and Saturday during the afternoon to evening hours. 
Otherwise, winds and seas are expected to remain below SCA levels 
through Sunday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...NONE.

&&

.HAZARD POTENTIAL OUTLOOK (FRI-TUE).

Increasing monsoon moisture may bring a chance of showers and
thunderstorms to the area next week.

&&

$$

PUBLIC...Phillips/RAT
AVIATION...Rorke
MARINE...Phillips/Sirard
SYNOPSIS...MW

weather.gov/losangeles